Aircraft gas turbine turbofan engines generally include a low pressure spool assembly having a fan rotor, low pressure compressor and a low pressure turbine connected by a low pressure spool shaft, and a high pressure spool assembly having a high pressure compressor and a high pressure turbine connected by a high pressure spool shaft which is hollow and disposed coaxially around the low pressure spool shaft. Conventionally, the fan rotor and the low pressure compressor, particularly a boost stage which is positioned upstream of the low pressure compressor, are tied together on the low pressure spool shaft, for example by a spline and a spigot arrangement. During flight, a bird strike event and other blade-off loads which create imbalanced loads to the fan rotor, may cause a fan rotor deflection. The fan rotor deflection may be transmitted downstream to the boost stage of the low pressure compressor to cause the boost stage to move with the fan rotor deflection, due to the fact that they are tied together on the low pressure spool shaft. The boost stage deflection affects tip clearance on the boost stage of the low pressure compressor, thereby further affecting the performance of the gas turbine engine.
Accordingly, there is a need to provide an improved fan rotor and boost compressor joint in aircraft gas turbine engines.